1. Field of the Invention
This invention relates to a method for determining an exposure condition of a photograph based on an image signal obtained by reading out an image recorded on a photographic film or the like.
2. Description of the Related Art
Japanese Unexamined Patent Publication No. 6(1994)-233052, discloses a photographic printer which reads on an image recorded on a photographic film, obtains an image signal made up of image signal components representing densities of respective picture elements modulates a light beam according to the image signal and records an image on a photosensitive material by scanning the photosensitive material with the modulated light beam.
In such a photographic printer, images are read out both from properly exposed films and underexposed or overexposed films, and recorded on photosensitive materials. In an improperly exposed film, a photographic image is recorded on the film using non-linear portions of the film such as a "foot portion" or a "shoulder portion" of the characteristic curve of the film. Accordingly, when an image signal read out from an improperly exposed film is used as the basis for recording an image on the photosensitive material, contrast of the recorded image becomes unsatisfactory in a high density region or a low density region.
In order to overcome such a problem, image signals read out from improperly exposed films have been subjected to nonlinear conversion processing with characteristics inverse to the characteristics of the film, where an image is recorded on a photosensitive material based on the processed image signal. See, for instance, Japanese National-Publication of-translated-version No. 4(1992)-504944.
When carrying out such a nonlinear conversion processing, it is necessary to know the exposure condition (properly exposed, underexposed or overexposed) of the film from which the image signal was read out, that is, what range of the characteristic curve of the film was used upon taking a photograph. For this purpose, there is disclosed, in the patent publication identified above, a method in which the exposure condition of a photographic film is determined based on a comparison of the image signal with the base density of the film.
However, using this method for determining the exposure condition, each photographic printer must be provided with its own density measuring means since the base density must be actually measured film-by-film. Consequently, the cost of the printer is increased. Furthermore, this method introduces delays into the film developing process since it takes a long time to determine the exposure condition.